Building energy usage and energy usage efficiency are areas of increasing concern due to rising energy costs. Energy efficient building components and intelligent building operation can make a great difference in the cost of operating a building over the building's lifetime.
Past energy efficiency efforts have led to many improvements in building construction. As a result, energy reduction efforts have begun to focus on reducing energy consumption in operation. Operational building efficiency has been enabled through computerized control of building systems such as lighting, heating, cooling, and other ventilation operations. By controlling lighting according to occupancy of a room or other building areas, the electrical consumption can be optimized and reduced, wherein room lighting levels are reduced or turned off completely if a room is not occupied.
Occupancy detection has typically employed motion-detecting occupancy sensors, such as ultrasonic motion sensors. Although ultrasonic motion detectors are inexpensive, detecting motion as a surrogate for occupancy has drawbacks. Ultrasonic sensors have a limited range and lose accuracy with increasing distance. Ultrasonic sensors have difficulty in detecting a number of occupants. Worse, if occupants of a room do not exhibit motion, or do not exhibit gross motions that are detectable as motion, ultrasonic motion detectors are known for turning off lights when a room is still occupied.
What is needed, therefore, is an occupancy sensor that is not dependent on motion detection.